MOBILE, Alabama -- Today marks a milestone in Hancock Holding Co.'s June purchase of Whitney Holding Co. -- the merger of the computer systems for both banking groups. That means customers who started with either bank can visit any Hancock or former Whitney branch to do business.

They've been able to use either bank's ATM since June.

"Overall, customers will enjoy more locations, more convenience, and more choices delivered by a top-performing bank with strong, solid, local ties," said Carl Chaney, Hancock president and CEO.

Gulfport-based Hancock decided to keep the Whitney name in Texas and Louisiana, where the New Orleans financial institution has a 100-plus year history. Given that, all signage on Hancock locations in Louisiana will convert to the Whitney brand starting today.

In Mobile and Baldwin counties, the new company is closing four branches -- Hancock's location on Dauphin Street in downtown Mobile, Schillinger Road in west Mobile and on U.S. Highway 98 in Daphne. A Whitney location on Dauphin Island Parkway will also close.

Hancock officials said that they sent notices to 244 Alabama customers telling them that the branches would close and advising them of other nearby locations.

The combined company's branches in Mississippi, Alabama and Florida will operate under the Hancock brand, and that signage will begin to change today as well.

Across the bank's five-state footprint, about 36 percent of customers will experience a change, while 64 percent will continue to bank under the brand they've known, the company said. As combined, the bank has $20 billion in assets and 258 branches.

"We'll end up now the thirty-second largest bank based in the US," Chaney said. "It's a significant transaction for Hancock."

Since the purchase was completed in June, a significant number of steps toward conversion have already been taken, Chaney said, including combining human resources, general ledger and trust systems.

With the assistance of consultants, Hancock went through two mock conversions prior to today.

Co-CEO John Hairston said it was a slow, thoughtful, and yes, expensive, approach is by design. He estimates the company spent about $125 million on merger expenses.

"This is not an 'everything happening in one night' event," Hairston said. "We've done a huge amount of work just about every weekend for the past five months."

Chaney and Hairston said with the Whitney acquisition under its belt, Hancock will look for other acquisition opportunities.